DV Gamma Decoding?

Streamworks Audio wrote on 11/9/2008, 5:01 PM

Hi folks,

Does anybody here know (google does not get me what I am after) if the Sony Vegas DV codec (or Vegas itself) applies gamma decoding (correction) when decoding a DV video? DV cams (for what I know) typically applies Gamma correction before compression following the Rec. 601 standard (1/2.2=.45).

What I am wondering is what are we looking at when we bring our DV clips into the time line? A gamma decoded color space? Or Gamma encoded color space?

Cheers!
Christopher

Comments

rs170a wrote on 11/9/2008, 5:14 PM

Check out Glenn Chan's website.
He has a few articles on the various colour spaces in Vegas that you might find useful.

Mike

Streamworks Audio wrote on 11/9/2008, 5:20 PM

Hi Mike,

Yeah great site indeed! Unfortunately this one question of mine was not answered ;-)

Thanks,
Chris

rs170a wrote on 11/9/2008, 6:03 PM

Chris, I wish I could be of more help but colour space issues isn't one of my strengths.
Hopefully someone who knows more than me will jump in here and answer your question.

Mike

GlennChan wrote on 11/9/2008, 6:50 PM

The camera will apply a transfer function (I'm actually not sure if this is standardized- I don't see it in Rec. 601, and some of the other standards apparently have wacky values). Your monitor/display will apply a transfer function that is roughly the opposite.

2- There is a small discrepancy between what the camera does and what a CRT monitor will do. This supposedly makes the image look "right".
Reading a book written by the people behind the NTSC standard (way back in 1953), the engineers were aware of this. I can't remember the details though.. I think they intended for this discrepancy to happen.
*Not everything in the original 1953 standard is followed today.

Some other discussion here:
http://www.poynton.com/notes/colour_and_gamma/GammaFAQ.html#gamma_correction

3- Read the linear light processing article on my website... it should tell you how to approach this from a practical point of view, and what the practical difference is (e.g. look at the pictures).

Streamworks Audio wrote on 11/9/2008, 7:02 PM

Thanks Glenn,

I am actually reading that one now... I am doing some tests bringing the DV clip back to linear (using levels with a gamma of 2.2222) before applying any color correction or further processing. The 32bit (1.0 or 2.2222) do not make a difference to the gamma of the DV clips on the time line. Doing a test using a MPEG2 clip shows a difference of the gamma.

Just wondering what Vegas was displaying... if it was decoded to show 1.0 gamma or not (which would be 2.2222 as the cam applied it). I am guessing it is decoded though... I image the 2.2222 encoded gamma would be far brighter than Vegas is showing.

*EDIT* You know I never thought about the monitors gamma... I guess even if it was at 2.2222 with the monitor it would look like 1.0

Thanks,
Chris